Antifreeze concentrates based on dicarboxylic acids, molybdate and triazoles or thiazoles, and coolant compositions comprising them

ABSTRACT

Antifreeze concentrates are based on a mixture of at least two different C3- to C16-dicarboxylic acids, molybdate and a mixture of at least two different triazoles or thiazoles.

The present invention relates to novel antifreeze concentrates based ona mixture of at least two different dicarboxylic acids, molybdate and amixture of at least two different triazoles or thiazoles. Furthermore,the present invention relates to ready-to-use aqueous coolantcompositions which comprise said antifreeze concentrates.

Radiator protection compositions for the coolant circulations ofinternal combustion engines, for example in automobiles, generallycontain alkylene glycols, especially ethylene glycol or propyleneglycol, as the main component. For use in the cooling system, they arediluted with water and, in addition to protection from freezing, shouldalso ensure good heat removal. Alkylene glycol/water mixtures arehowever very corrosive at the operating temperatures of internalcombustion engines, and it is for this reason that the various metals,for example copper, brass, iron, steel, cast iron (gray cast iron),lead, tin, chromium, zinc, aluminum, magnesium and the alloys thereof,and solder metals, such as tin solder (soft solder), which may occur inthe cooling system, have to be adequately protected from the varioustypes of corrosion, for example pitting, crevice corrosion, erosion orcavitation. The prior art has disclosed a large number of individualchemical substances for use as corrosion inhibitors in such coolingsystems.

Antifreezes based on ethylene glycol and containing carboxylic acids,alkali metal molybdate and triazoles or thiazoles are disclosed in EP-B552 988 (1), DE-A 34 13 416 (2), U.S. Pat. No. 4,561,990 (3) and DE-A195 47 499 (4).

The operating conditions in modern internal combustion engines mean thattoday the corrosion protection capability and in particular thehigh-temperature stability of the coolant have to meet very much higherrequirements than in the past with regard to thermal stress on the heattransfer surfaces, pressure and flow rate as well as the choice of amaterial. The known prior art compositions are unsatisfactory in thisrespect.

It is an object of the present invention to provide appropriateantifreeze concentrates which do not have the disadvantages of the priorart.

We have found that this object is achieved by antifreeze concentratesbased on alkylene glycols or derivatives thereof, which contain

(a) from 0.05 to 10, preferably from 0.1 to 5, % by weight, based on thetotal amount of the concentrate, of a mixture of at least two differentdicarboxylic acids, each of 3 to 16 carbon atoms, in the form of theiralkali metal, ammonium or substituted ammonium salts,

(b) from 0.01 to 5, preferably from 0.05 to 2, % by weight, based on thetotal amount of the concentrate, of one or more alkali metal, ammoniumor substituted ammonium molybdates and

(c) from 0.01 to 3, preferably from 0.05 to 1, % by weight, based on thetotal amount of the concentrate, of a mixture of at least two differentcorrosion inhibitors selected from the group consisting of thehydrocarbon-triazoles and the hydrocarbon-thiazoles.

The novel antifreeze concentrates can be used wherever the protection ofwater-containing systems from freezing (as a rule for the range from 0to −40° C., in particular from −20 to −35° C.) and simultaneously thecorrosion protection of the metal housings of water-containingcontainers are to be ensured. The cooling circulations of internalcombustion engines, in particular in automobiles, such as cars andtrucks, are of particular interest here. However, the novel antifreezeconcentrates can also be used for said purpose in stationary engines, inhot water circulations of central heating systems, in radiators heatedby electrical resistors and in solar heating circulations.

In a preferred embodiment, the component (a) is a mixture of twodifferent saturated aliphatic dicarboxylic acids, each of 3 to 16,preferably each of 4 to 12, carbon atoms.

Typical examples of such dicarboxylic acids are malonic acid, succinicacid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaicacid, sebacic acid, undecanedioic acid, dodecanedioic acid,dicyclopentadienedicarboxylic acid, phthalic acid and terephthalic acid.Corresponding imides, e.g. succinimide, may be also be used here.

A mixture of succinic acid and sebacic acid is particularly preferredfor the component (a).

In a further preferred embodiment, the component (c) is a mixture of twodifferent hydrocarbon-triazoles, in particular of benzotriazole andtoluotriazole. However, a mixture of two hydrocarbon-thiazoles or of onehydrocarbon-triazole and one hydrocarbon-thiazole may also be used.Examples of suitable hydrocarbon-thiazoles are benzothiazole and2-mercaptobenzothiazole.

In a further embodiment, the novel antifreeze concentrates additionallycontain

(d) from 0.05 to 5, preferably from 0.1 to 3, % by weight, based on thetotal amount of the concentrate, of one or more aliphatic or aromaticmonocarboxylic acids, each of 5 to 18 carbon atoms, in the form of theiralkali metal, ammonium or substituted ammonium salts.

Examples of suitable such linear or branched aliphatic monocarboxylicacids are pentanoic acid, hexanoic acid, octanoic acid, 2-ethylhexanoicacid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid andlinolenic acid.

Suitable such aromatic monocarboxylic acids are in particular benzoicacid, as well as, for example, C₁-C₈-alkylbenzoic acids, such as o-, m-or p-methylbenzbic acid or p-tert-butylbenzoic acid, andhydroxyl-containing aromatic monocarboxylic acids, such as o-, m- orp-hydroxybenzoic acid or o-, m- or p-(hydroxymethyl)benzoic acid.

Aromatic monocarboxylic acids of 6 to 10 carbon atoms which may containhydroxyl groups are particularly preferred as component (d).

All stated carboxylic acids are present as alkali metal salts,especially as sodium or potassium salts, as ammonium salts or assubstituted ammonium salts (amine salts), for example trialkylamines ortrialkanolamines.

Furthermore, the novel antifreeze concentrates may additionally containone or more corrosion inhibitors selected from the group consisting ofthe alkali metal borates, alkali metal phosphates, alkali metalchromates, alkali metal silicates, alkali metal nitrites, alkali metalnitrates and magnesium nitrate in amounts of, in each case, up to 1, inparticular from 0.01 to 0.8, % by weight, based on the total amount ofthe concentrate.

Examples of such additional corrosion inhibitors are sodium tetraborate(borax), disodium hydrogen phosphate, trisodium phosphate, sodiummetasilicate, sodium nitrite and sodium nitrate.

When alkali metal silicates are present, they are expediently stabilizedby conventional organosilicosulfonates in conventional amounts.

In addition to said inhibitor components, for example, soluble magnesiumsalts of organic acids, e.g. magnesium benzenesulfonate, magnesiummethanesulfonate, magnesium acetate or magnesium propionate,hydrocarbazoles or quaternized imidazoles, as described in DE-A 196 05509, may also be used in conventional amounts as further inhibitors.

Furthermore, the novel antifreeze concentrates may additionally containup to 1, in particular from 0.01 to 0.5, % by weight, based on the totalamount of the concentrate, of hard water stabilizers based onpolyacrylic acid, polymaleic acid, acrylic acid/maleic acid copolymers,polyvinylpyrrolidone, polyvinylimidazole,vinylpyrrolidone/vinylimidazole copolymers and/or copolymers ofunsaturated carboxylic acids and olefins.

However, low molecular weight compounds, for example polycarboxylicacids, such as 2-phosphonobutane-1,2,4-tricarboxylic acid, may also beused as hard water stabilizers or sequestering agents.

The pH of the novel antifreeze concentrates is usually from 6 to 11,preferably from 7 to 10, in particular from 7.5 to 9, especially from7.5 to 8.3. The desired pH is as a rule established by adding alkalimetal hydroxide, ammonia or amines to the formulation; solid sodiumhydroxide or potassium hydroxide and aqueous sodium hydroxide orpotassium hydroxide solution are particularly suitable for this purpose.Carboxylic acids which are to be present are expediently added directlyas corresponding alkali metal salts in order automatically to be in thedesired pH range; however, the carboxylic acids may also be added asfree acids and then neutralized with alkali metal hydroxide, ammonia oramines, and the desired pH established.

Dicarboxylic acids used are preferably (completely or predominantly)present as dipotassium salts in the novel antifreeze concentrates, whichresults in an optimum alkalinity reserve of the formulation. Either therelevant acids are added directly as dipotassium salts or the freedicarboxylic acids in the formulation are neutralized with potassiumhydroxide. When a mixture of succinic acid and sebacic acid is used,both may be present as dipotassium salts or the succinic acid as thedipotassium salt and the sebacic acid as the disodium salt. Depending onthe dicarboxylic acid and pH used, minor amounts of the respectiveacidic mono-alkali metal-hydrogen salts may also be present, inparticular when sodium hydroxide is used as the neutralizing agent.

Suitable liquid alcoholic freezing point depressants, which usuallyaccount for the main part (as a rule at least 75, particularly at least85, % by weight) of the novel antifreeze concentrates, are alkyleneglycols and derivatives thereof, in particular propylene glycol andespecially ethylene glycol. However, higher glycols and glycol ethersare also suitable, e.g. diethylene glycol, dipropylene glycol andmonoethers of glycols such as the methyl, ethyl, propyl and butyl etherof ethylene glycol, propylene glycol, diethylene glycol and dipropyleneglycol. Mixtures of said glycols and glycol ethers may also be used.

In a preferred embodiment, the novel antifreeze concentrates are basedon ethylene glycol or mixtures of alkylene glycols which contain atleast 95% by weight of ethylene glycol.

As further conventional assistants, the novel antifreeze concentratesmay also contain, in conventional small amounts, antifoams (as a rule inamounts from 0.003 to 0.008% by weight), dyes and bitter substances forreasons of hygiene and of safety in the event of swallowing (for exampleof the denatonium benzoate) type.

The preparation of the novel antifreeze concentrates can be effected bymixing together said components in principle in any desired sequence. Ina typical method of preparation the neutralizing agent, in particularsodium hydroxide or potassium hydroxide, is first dissolved in a part,for example half, the total amount of alkylene glycol. Thereafter, thetwo dicarboxylic acids are added in free form, for example firstsuccinic acid and then sebacic acid. After these have dissolved to forma clear solution without residue, the remaining alkylene glycol isadded. The remaining components are incorporated into the formulationeither at the end or together with the dicarboxylic acids.

Particularly preferred novel antifreeze concentrates have the followingcomposition:

from 0.5 to 3, in particular from 1.5 to 2, % by weight of succinic acid

from 0.5 to 3, in particular from 1.5 to 2, % by weight of sebacic acid

from 0.05 to 1, in particular from 0.1 to 0.5, % by weight of sodiummolybdate or potassium molybdate

from 0.05 to 0.5, in particular from 0.05 to 0.25, % by weight ofbenzotriazole

from 0.05 to 0.5, in particular from 0.05 to 0.25, % by weight oftoluotriazole

from 0.1 to 2, in particular from 0.2 to 1, % by weight of benzoic acid

from 0 to 5, in particular from 0.1 to 2, % by weight of demineralizedwater

corresponding amounts of sodium hydroxide or potassium hydroxide forbringing the pH to 7.5 to 9

as the remainder to 100% by weight, monoethylene glycol or a mixture ofalkylene glycols containing at least 85% by weight of monoethyleneglycol.

The present invention also relates to ready-to-use aqueous coolantcompositions having a reduced freezing point, in particular for radiatorprotection in the automotive sector, which comprise water and from 10 to90, in particular from 20 to 60, % by weight of the novel antifreezeconcentrates.

The novel antifreeze concentrates are distinguished by effectivecorrosion inhibition of the metals and alloys listed at the outset. Theyare also readily compatible with further materials, such as rubbers,plastics, glue joints, fiber and rubber seals and similar materialswhich may occur in plants or internal combustion engines, and give goodresults in electrochemical corrosion tests.

In particular, however, the novel antifreeze concentrates aredistinguished by improved high-temperature stability to the prior artcompositions. At temperatures of 160° C. or higher, the systems remainstable and give reproducible test results, for example at 175° C.

The examples which follow illustrate the invention without restrictingit.

EXAMPLES

The radiator protection concentrate formulation A shown below in Table 1was used as novel antifreeze concentrate and a formulation analogous toExample 1 of EP-B 552 988 (1) was used as comparative formulation B.

TABLE 1 Compositions of the antifreeze concentrates [% by weight]Formulation A Formulation B Monoethylene glycol 91.80 93.96 Water 0.750.47 Succinic acid 1.82 — Sebacic acid 1.82 1.50 Itaconic acid — 0.70Sodium molybdate dihydrate 0.20 0.90 Benzotriazole 0.15 — Toluotriazole0.10 0.10 Sodium benzoate 0.40 — Potassium hydroxide 2.96 — Sodiumhydroxide (50% strength — 2.06 by weight) Magnesium nitrate hexahydrate— 0.30 Conventional hard water — 0.01 stabilizer (Bayhibit AM)

Formulations A and B were subjected in aqueous dilution to aconventional corrosion test and a high-temperature stability test.

The results in the corrosion test according to ASTM D 1384 are shown inTable 2. They show that the novel formulation A has just as good aprotective effect in the case of nonferrous metals, such as copper andbrass, and the case of other metals, such as soft solder, steel, graycast iron and cast aluminum, as the comparative formulation B andremoval of material occurs in virtually no case.

TABLE 2 Glassware corrosion tests according to ASTM D 1384 Formulation AFormulation B Weight change Weight change Test specimen [mg/cm²][mg/cm²] Copper −0.01 +0.01 Soft solder 0 +0.02 Brass −0.01 +0.01 Steel0 +0.02 Gray cast iron +0.06 +0.09 Cast aluminum +0.06 +0.04

In these corrosion tests, the concentration for each of the twoformulations was 33% by volume in water.

In high-temperature stability tests for radiator protection compositions(“Tenue en Temperature d'un Liquide de Refroidissement”) according toPSA standard D 55 5345 (comparable with Experimental Test Method CECC-14-X-99 of Mar. 18, 1999), the effect of the temperature on the pHstability and on the pressure is determined. The sharper the increase inthese two parameters, the greater the extent to which the corrosioninhibitors contained in the radiator protection formulation undergodecomposition.

For this purpose, 660 ml of the radiator protection concentrateformulation A or B diluted to 33% by volume in water were introducedinto a closed aluminum pressure-resistant container in which a cast ironring was also present as a second metal, and were left to stand at 175°C. for 192 hours while stirring. At specific time intervals, thepressure was measured, samples were taken and the pH of the samples wasdetermined. After the end of the test an additional visual assessmentwas carried out to determine whether deposits or corrosion had occurredon the metal surfaces. 24 hours after completion of the test, the volumeof the residue in the liquid was also determined.

The results of this high-temperature stability test are shown in Table3. While the pH and the pressure remained virtually constant when thenovel formulation A was used, both parameters increased substantiallyand a precipitate formed on the aluminum surface when the comparativeformulation B was used, and at the same time a considerably greaterresidue was also found here in the test liquid.

TABLE 3 High-temperature stability test according to PSA standard D 555345 Formulation A Formulation B Run time Pressure Pressure [h] pH [bar]pH [bar] 0 7.90 7.0 8.03 6.8 8 7.64 7.0 6.85 6.8 24 7.59 7.1 6.92 6.9 487.57 7.2 8.66 7.0 72 7.58 7.2 9.52 7.2 144 7.96 7.4 10.32 8.0 192 8.207.5 10.40 9.5 Visual assessment: Aluminum no deposit white deposit Castiron no deposit no deposit Volume of the 3 ml 7 ml residue

These results show that the novel antifreeze concentrates havesubstantially improved high-temperature stability in combination with anequally good corrosion protection effect compared with the prior art.

What is claimed is:
 1. An antifreeze concentrate comprising one or morealkylene glycols or one or more derivatives thereof, and (a) from 0.05to 10% by weight, based on the total weight of the concentrate, of amixture of at least two different dicarboxylic acids each having from 3to 16 carbon atoms in the form of their alkali metal salts, ammoniumsalts, substituted ammonium salts, or, in the case of saturatedaliphatic dicarboxylic acids having from 3 to 16 carbon atoms, theirimides, (b) from 0.01 to 5% by weight, based on the total weight of theconcentrate, of one or more alkali metal molybdates, ammonium molybdatesor substituted ammonium molybdates, and (c) from 0.01 to 3% by weight,based on the total weight of the concentrate, of a mixture of at leasttwo different corrosion inhibitors selected from the group consisting ofhydrocarbon triazoles and hydrocarbon thiazoles.
 2. The antifreezeconcentrate as claimed in claim 1 in which the component (a) is amixture of two different saturated aliphatic dicarboxylic acids eachhaving from 3 to 16 carbon atoms.
 3. The antifreeze concentrate asclaimed in claim 1 in which the component (c) is a mixture of twodifferent hydrocarbon triazoles.
 4. The antifreeze concentrate asclaimed in claim 1 which further comprises (d) from 0.05 to 5% byweight, based on the total weight of the concentrate, of one or morealiphatic or aromatic monocarboxylic acids each having from 5 to 18carbon atoms in the form of their alkali metal salts, ammonium salts orsubstituted ammonium salts.
 5. The antifreeze concentrate as claimed inclaim 1 which further comprises one or more corrosion inhibitorsselected from the group consisting of alkali metal borates, alkali metalphosphates, alkali metal silicates, alkali metal nitrites, alkali metalnitrates and magnesium nitrate, in amounts of in each case up to 1% byweight, based on the total weight of the concentrate.
 6. The antifreezeconcentrate as claimed in claim 1 which further comprises up to 1% byweight, based on the total weight of the concentrate, of one or morehard water stabilizers based on polyacrylic acid, polymaleic acid,acrylic acid-maleic acid copolymers, polyvinylpyrrolidone,polyvinylimidazole, vinylpyrrolidone-vinylimidazole copolymers,copolymers of unsaturated carboxylic acids, copolymers of olefins, ormixtures thereof.
 7. The antifreeze concentrate as claimed in claim 1having a pH in the range from 6 to
 11. 8. The antifreeze concentrate asclaimed in claim 1 comprising ethylene glycol or a mixture of alkyleneglycols containing at least 95% by weight of ethylene glycol.
 9. Aready-to-use aqueous coolant composition having a depressed freezingpoint which comprises water and from 10 to 90% by weight of theantifreeze concentrate as claimed in claim
 1. 10. The antifreeze ofclaim 1, wherein the one or more alkylene glycols is an alkylene glycolderivative.
 11. The antifreeze concentrate of claim 2, wherein thealiphatic dicarboxylic acids each have from 4 to 12 carbon atoms. 12.The antifreeze concentrate of claim 3, wherein component (c) is amixture of benzotriazole and toluotriazole.
 13. The antifreezeconcentrate as claimed in claim 1, wherein the two differentdicarboxylic acids are selected from the group consisting of malonicacid, succinic acid, glutaric acid, adipic acid, pimelic acid, subericacid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioicacid, dicyclopentadienedicarboxylic acid, phthalic acid and terephthalicacid.
 14. The antifreeze concentrate as claimed in claim 1, wherein thedicarboxylic acids are succinic acid and sebacic acid.
 15. Theantifreeze concentrate as claimed in claim 1, wherein the at least twodifferent corrosion inhibitors are benzothiazole and2-mercaptobenzothiazole.
 16. The antifreeze concentrate as claimed inclaim 1, wherein the dicarboxylic acids are present as dipotassiumsalts.
 17. The composition as claimed in claim 1, comprising: from 0.5to 3% by weight of succinic acid, from 0.5 to 3% by weight of sebacicacid, from 0.05 to 1% by weight of at least one of sodium molybdate orpotassium molybdate, from 0.05 to 0.5% by weight of benzotriazole, from0.05 to 0.5% by weight of toluotriazole, from 0.1 to 2% by weight andbenzoic acid, and from 0 to 5% by weight of demineralized water.
 18. Theantifreeze concentrate as claimed in claim 1, comprising from 1.5 to 2%by weight of succinic acid, from 1.5 to 2% by weight of sebacic acid,from 0.1 to 0.5% by weight of at least one of sodium molybdate orpotassium molybdate, from 0.05 to 0.25% by weight of benzotriazole, from0.05 to 0.25% by weight of toluotriazole, from 0.2 to 1% by weight ofbenzoic acid, and from 0.1 to 2% by weight of demineralized water,wherein the one or more alkylene glycols comprises at least 85% byweight of monoethylene glycol.